Antimicrobial surveillance – BRD pathogens

Summary

Using culture and susceptibility testing for surveillance of antimicrobial resistance is a key pillar of Antimicrobial Stewardship, as outlined in the 2018 edition of the ALFA-MLA Antimicrobial stewardship guideline for the Australian cattle feedlot industry.

This project conducted pilot surveillance of resistance of bovine respiratory disease (BRD) pathogens to common veterinary antimicrobial agents across seven Australian feedlots in 2019, to encourage the adoption of best practice antimicrobial stewardship practices by the industry.

The main BRD-causing bacteria tested for antimicrobial resistance in order of prevalence included: Pasteurella multocida, Mannheimia hemolytica, Histophilus somni and Mycoplasma bovis.

For the first time in Australia, low levels of resistance were found in Pasteurella multocida (23.1%) to the macrolide class of antimicrobials. Whilst resistance levels are low by international standards, feedlots should embrace antimicrobial stewardship principals to reduce the risk of developing further resistance.

Objectives

• Develop guidelines and training materials for the collection of diagnostic specimens from cases of BRD by feedlot staff for antimicrobial culture and susceptibility testing.
• Undertake case sampling studies at seven Australian feedlots that differ in their antimicrobial treatment regimes during 2018/2019 BRD seasons to link clinical, epidemiological and pathological data with microbiological culture and susceptibility testing.

Key findings

• The main BRD-causing bacteria tested for antimicrobial resistance in order of prevalence included: Pasteurella multocida, Mannheimia hemolytica, Histophilus somni.
• Trueperella pyogenes was commonly isolated as a cause of secondary infection.
• Most bacteria tested were sensitive to all tested antimicrobial agents. H. somni isolates were pan susceptible all antimicrobials tested. M. haemolytica isolates were pan susceptible to all antimicrobials tested that had Clinical Laboratory Standards Institute (CLSI) break points available except for a single isolate from the 2019 collection.
• For the first time in Australia, low levels of resistance were found in Pasteurella multocida (23.1%) to the macrolide class of antimicrobials. Resistance to tetracycline (16.9%) was also identified.

Benefits to industry

This project has enabled antimicrobial culture and susceptibility testing for the Australian feedlot industry through collaboration between lot feeders, diagnostic laboratories, researchers and consulting veterinarians. Feedlots are now equipped to conduct their own local antimicrobial resistance (AMR) surveillance and integrate the findings into their antimicrobial stewardship programmes.

MLA action

MLA has communicated the results of this research to feedlot veterinarians during the ALFA-MLA Vets and Nutritionists meeting in March, 2020. Further communication of the project will occur during face to face visits of the ALFA-MLA Technical Services Officer to all NFAS accredited feedlots.

Further whole of genome sequencing is occurring to identify resistance mechanisms in Pasteurella multocida isolates from this project.

Future research

In practical terms, feedlots should:

• implement an antimicrobial stewardship plan with their consulting veterinarian based on the antimicrobial stewardship principals to reduce risk of further resistance developing
• conduct a routine antimicrobial resistance surveillance program each year
• look for viable preventatives (e.g. vaccines, backgrounding system prior to feedlot entry) and alternatives to lower the use of medically important antimicrobials
• conduct internal feedlot reporting to monitor the use and total quantity of antimicrobials.

Related resources

MLA guides

Antimicrobial stewardship guidelines for the cattle feedlot industry

Tips and Tools – Summary of Bovine Respiratory Disease preventative practices

Evaluation of practices used to reduce the incidence of bovine respiratory disease in Australian feedlots